This application is based on Japanese Patent Application No. 11-288270 filed Oct. 8, 2000, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a braking system.
2. Discussion of Related Art
JP-A-5-65060 discloses an example of a braking system, which includes (1) a brake cylinder, (2) a master cylinder operable by a brake operating member, for mechanically pressurizing a working fluid such that the pressure of the pressurized fluid corresponds to an operating force acting on the brake operating member, (3) a power-operated hydraulic pressure source operable with an electric energy supplied thereto, for generating a braking force corresponding the operating force of the brake operating member, and (4) a fluid-communication switching device for fluid communication of the brake cylinder with the power-operated hydraulic pressure source when the power-operated hydraulic pressure source is normal, and with the master cylinder when the power-operated hydraulic pressure source is defective. In this braking system, the power-operated hydraulic pressure source is arranged such that the pressure of the fluid pressurized by the power-operated hydraulic pressure source is higher than that of the fluid pressurized by the master cylinder. Accordingly, when the brake cylinder which has been held in communication with the power-operated hydraulic pressure source is brought into communication with the master cylinder upon detection of a defect of the power-operated hydraulic pressure source, the braking force corresponding to a given operating force of the brake operating member varies unexpectedly to the operator of an automotive vehicle on which the braking system is provided.
It is therefore an object of the present invention to provide a braking system which is arranged to minimize a change in the braking force which is unexpected to the vehicle operator.
The above object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking system comprising:
a brake cylinder;
a first hydraulic pressure source including a first pump device operable to pressurize a working fluid;
a second hydraulic pressure source operable in response to an operation of a brake operating member, to pressurize the fluid to a pressure higher than a value corresponding to an operating force acting on the brake operating member;
a brake-cylinder-pressure control device operable when the brake cylinder is disconnected from the second hydraulic pressure source, to control the pressure of the fluid pressurized by the first hydraulic pressure source, for thereby controlling a pressure of the fluid in the brake cylinder to a value determined on the basis of the operating force; and
an emergency communication device operable when at least one of the brake-cylinder-pressure control device and the first pump device fails to normally function, to hold the brake cylinder in communication with the second hydraulic pressure source.
When the brake operating member is operated in the braking system according to the above mode (1) of this invention, the pressure of the fluid pressurized by the first hydraulic pressure is controlled by the brake-cylinder-pressure control device while the brake cylinder is disconnected from the second hydraulic pressure source, such that the fluid pressure in the brake cylinder is controlled to a value determined by the operating force of the brake operating member. The brake-cylinder-pressure control device may be adapted to control the first pump device of the first hydraulic pressure source, to thereby control the fluid pressure in the brake cylinder. Alternatively, the brake-cylinder-pressure control device may include a solenoid-operated control valve for controlling the fluid pressure in the brake cylinder, and a control-valve control device for controlling the solenoid-operated control valve.
Where at least one of the brake-cylinder-pressure control device and the first pump device of the first hydraulic pressure source fails to normally function, the brake cylinder is brought into fluid communication with the second hydraulic pressure source. When the brake operating member is operated, the second hydraulic pressure source pressurizes the fluid to a pressure higher than a value corresponding to the operating force of the brake operating member, and the thus pressurized fluid is delivered to the brake cylinder. Thus, the fluid pressure in the brake cylinder can be made higher in the present braking system than in a braking system in which the second hydraulic pressure source pressurizes the fluid to a pressure value corresponding to the operating force of the brake operating member. This arrangement is effective to reduce the amount of unexpected change of the braking force corresponding to a given amount of operating force of the brake operating member, which unexpected change takes place due to a defect of the brake-cylinder-pressure control device and/or the first pump device.
The first pump device fails to normally function when there is any one of defects such as: a defect (e.g., excessive voltage drop) of the electric power source provided to supply the first pump device with an electric energy; a defect of an electric motor of the first pump device; a defect of a control device (including a driver circuit, and a computer) for controlling the electric motor; and a defect of any sensor for detecting the operating state (e.g., rotating speed) of the electric motor. Where the brake-cylinder-pressure control device includes a solenoid-operated control valve and a control-valve control device for controlling the control valve, the brake-cylinder-pressure control device fails to normally function when there is any one of defects such as: a defect of a solenoid-operated control valve; a defect of an electric power source used to control the control valve; a defect of the control-valve control device; and a defect of any sensor used for controlling the control valve to control the fluid pressure in the brake cylinder. Where the brake-cylinder-pressure control device includes a controller adapted to control the first pump device of the first hydraulic pressure source so as to control the fluid pressure in the brake cylinder, the brake-cylinder-pressure control device fails to normally function when there is any one of defects such as: a defect of the controller; and a defect of any sensor used to control the first pump device.
(2) A braking system according to the above mode (1), wherein the second hydraulic pressure source includes at least one of a booster for boosting the operating force of the brake operating member, and a pressure-increasing device for increasing the pressure of the fluid pressurized when the brake operating member is operated, the braking system further comprising an energy storing portion for storing an energy to be used to operate at least one of the booster and the pressure-increasing device.
In the braking system according to the above mode (2) wherein the energy storing portion is provided, the pressure-increasing device and/or the booster of the second hydraulic pressure source can be operated by the energy stored in the energy storing portion, even if the braking system becomes unable to generate an energy due to an electrical failure, for instance. Thus, the pressure of the fluid pressurized by the second hydraulic pressure source can be increased to a value higher than a value corresponding to the operating force of the brake operating member, so that the amount of change of the braking force which is unexpected to the vehicle operator can be reduced, when the brake cylinder is brought into communication the second hydraulic pressure source, in the event of a failure of the brake-cylinder-pressure control device and/or the first pump device.
The energy storing portion may be adapted to store an energy generated by the braking system per se, or an energy generated by a suitable drive other than the braking system, such as a drive device for driving an automotive vehicle, and a steering device or air-suspension device provided in an automotive vehicle. In the former case, the energy storing portion may be an accumulator provided to store a highly pressurized fluid delivered from the first pump device of the first hydraulic pressure source. In the latter case, the energy storing portion may be any one of: a vacuum tank storing a negative air pressure generated during an operation of an engine of an automotive vehicle; a battery for storing an electric energy generated by an electric generator (alternator) driven by a vehicle engine; a battery for storing an electric energy generated by an electric motor used for driving an electric or hybrid vehicle, when the electric motor is operated in a regenerative braking mode; an accumulator for storing a working fluid pressurized by a pump device of a power steering device of an automotive vehicle, which pump device is driven by an engine; and an air tank (pneumatic accumulator) for storing a compressed air generated by a compressor used in an air suspension system provided in an automotive vehicle. In any case, a considerable portion of the energy generated in an automotive vehicle is generated by consumption of an electric energy. The energy storing portion indicated above is provided to store an energy while the electric system of the vehicle is normal, so that the energy stored in the energy storing portion can be subsequently used in the event of an electrical failure.
Further, the energy storing portion may be a solar battery or cell arranged to store a solar energy. Where the solar cell is used, the amount of consumption of the energy generated by the vehicle can be can be reduced.
The second hydraulic pressure source may include only one of the pressure-increasing device and the booster, or both of them.
(3) A braking system according to the above mode (2), wherein the first hydraulic pressure source includes a first accumulator for storing a pressurized hydraulic fluid as the working fluid pressurized by the first pump device, and wherein the first accumulator serves as the energy storing portion, and the above-indicated at least one of said pressure-increasing device and the booster is hydraulically operated with the pressurized hydraulic fluid stored in the first accumulator.
In the braking system according to the above mode (3), the above-indicated one of the pressure-increasing device and the booster is a hydraulically operated device, and therefore can be operated with the pressurized hydraulic fluid or liquid stored in the first accumulator. When the first pump device of the first hydraulic pressure source fails to normally function, the first hydraulic pressure source is disconnected from the brake cylinder, so that the pressurized hydraulic fluid stored in the first accumulator of the first hydraulic pressure source can be used to activate the brake cylinder while the first hydraulic pressure source is defective. This arrangement permits effective utilization of the hydraulic energy. Further, the pressurized hydraulic fluid can be rapidly supplied from the first accumulator to the hydraulically operated pressure-increasing device and/or booster, thereby assuring activation of the brake cylinder with a reduced delay. In addition, the use of the first accumulator as the energy storing portion, the second hydraulic pressure source need not be provided with an energy storing portion for storing the hydraulic energy for operating the pressure-increasing device and/or the booster, whereby the braking system is available at a reduced cost and can be small-sized.
(4) A braking system according to the above mode (3), wherein the first accumulator has a large storing capacity.
In the braking system according to the above mode (3), the first accumulator is capable of storing a large amount of the pressurized hydraulic fluid, the pressure-increasing and/or the booster can be operated for a comparatively long total operating time after the brake cylinder is brought into communication with the second hydraulic pressure source. If the braking system is provided with an alarm indicator informing the vehicle operator that the brake-cylinder-pressure control device and/or the first pump device fails to normally function, the vehicle operator can drive the vehicle to a suitable place for repairing the braking system, while the vehicle is braked as needed with the brake cylinder being activated with the pressurized hydraulic fluid stored in the first accumulator.
Preferably, the first accumulator has a storing capacity sufficient to enable at least one of the pressure-increasing device and the booster to operate even after the brake cylinder has been operated ten or more times, for instance. The storing capacity of the first accumulator is desirably determined in view of the size of the braking system, and the expected number of operations of the brake cylinder generally required for driving the vehicle to a repairing station.
(5) A braking system according to any one of the above modes (1)-(4), wherein the second hydraulic pressure source includes a hydraulic booster hydraulically operated to boost the operating force of the brake operating member,
and wherein the hydraulic booster includes a pressure regulating portion for regulating the pressure of the fluid received from an accumulator, to a value corresponding to the operating force of the brake operating member, and further includes a power piston operatively connected to the brake operating member, the hydraulic booster having a booster chamber which is partially defined by the power piston and located rearwardly of the power piston as viewed in a direction in which the power piston is advanced when the brake operating member is operated, the booster chamber receiving the fluid whose pressure has been regulated by the pressure regulating portion, such that a drive force corresponding to the pressure of the fluid in the booster chamber acts on the power piston in the direction, whereby the operating force of the brake operating member is boosted.
One preferred form of the hydraulic booster included in the second hydraulic pressure source will be described in the DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.
The accumulator described above with respect to the pressure regulating portion of the hydraulic booster may be the first accumulator of the first hydraulic pressure source, which has been described above with respect to the braking system according to the above mode (3).
(6) A braking system according to the above mode (5), comprising a plurality of brake cylinders as the above-indicated brake cylinder, and wherein at least one of the plurality of brake cylinders is connected to the booster chamber while the other (52, 54, 292, 296) of the plurality of brake cylinders is connected to a pressurizing chamber which is partially defined by a pressurizing piston and located frontwardly of the pressurizing piston as viewed in the above-indicated direction, the pressurizing piston being operatively connected to the power piston.
Where the braking system has two mutually independent brake application sub-systems, a first group of at least one brake cylinder included in one of the two brake application sub-systems is connected to the booster chamber of the hydraulic booster, while a second group of at least one brake cylinder is connected to the pressurizing chamber. Even when the accumulator from which the booster chamber receives the pressurized fluid is defective, the fluid pressure in the pressurizing chamber can be increased to a value corresponding to the operating force of the brake operating member. In this respect, the braking system wherein the two brake application sub-systems respectively correspond to a pair of front wheels and a pair of rear wheels of an automotive vehicle, for example, is preferably arranged such that the pressurizing chamber is connected to the brake cylinders for the front wheels.
(7) A braking system according to the above mode (2), wherein the second hydraulic pressure source includes a vacuum booster operable with a negative pressure to boost the operating force of the brake operating member, and the energy storing portion includes a vacuum tank for storing the negative pressure.
In the braking system according to the above mode (7), the vacuum booster included in the second hydraulic pressure source is operated with a negative pressure to boost the operating force of the brake operating member. The vacuum tank may be adapted to store a negative pressure generated while an engine of an automotive vehicle is operated. The vacuum tank may be exclusively used for the braking system. Alternatively ,the vacuum tank may be surging tank provided in an engine assembly of the vehicle.
The engine of an automotive vehicle is not always in operation while the vehicle is able to run (e.g., while the ignition switch is on). For instance, the vehicle is placed in an ecology-oriented mode in which the engine is off, while a predetermined condition is satisfied, for instance, while the absence of an intention of the vehicle driver to start the stationary vehicle is detected. Where the engine is frequently turned off under such a condition of the vehicle, the pressure in the vacuum tank may rise towards the atmospheric level. Where the vehicle is a hybrid vehicle, the engine is not always in operation, and the pressure in the vacuum tank may rise towards the atmospheric pressure. Even when the engine is held in operation, the throttle valve is frequently placed in the fully open position, where the engine is operated in a fuel-lean state. In this case, too, the pressure in the vacuum tank may rise towards the atmospheric level. In any of the above-indicated cases, it is desirable to turn on the engine or limit the opening of the throttle valve, when the pressure in the vacuum tank has exceeded a predetermined upper limit which is relatively close to the atmospheric level.
The braking system according to the above mode (7) wherein the energy generated by a device not included in the braking system is utilized is not required to generate the energy for the purpose of operating the vacuum booster. Accordingly, the overall energy efficiency of the vehicle can be improved. Even in the event of an electrical failure of the braking system, the vacuum booster can be operated with a negative pressure.
(8) A braking system according to the above mode (2), wherein the second hydraulic pressure source includes an electrically operated booster operable with an electric energy to boost the operating force of the brake operating member, and the energy storing portion includes a battery for storing the electric energy.
In the braking system according to the above mode (8), the second hydraulic pressure source includes an electrically operated booster operable for boosting the operating force of the brake operating member. As described in detail in the DESCRIPTION OF THE PREFERRED EMBODIMENTS, the electrically operated booster may utilize a drive force produced by an electric motor, or an electromagnetic force produced by a coil and a magnet. The battery serving as the energy storing portion may be a battery for storing an electric energy generated by an electric generator driven by an engine. Where the vehicle drive assembly includes an electric motor for driving an automotive vehicle, the battery serving as the energy storing portion may be a battery for storing an electric energy generated when the electric vehicle drive motor is operated in a regenerative braking mode. The battery serving as the energy storing portion may be a battery included in the vehicle drive assembly, or a battery provided exclusively for operating the electrically operated booster. In the latter case, the operating reliability of the electrically operated booster is improved. In any cases described above, the battery serving as the energy storing portion for operating the electrically operated booster is different or separate from the battery used for supplying the first pump device of the first hydraulic pressure source with an electric energy. This arrangement enables the electrically operated booster to be operated even when the first pump device is not able to normally operate due to a defect of the electric power source used for the first pump device. The battery for operating the electrically operated booster may be a solar cell. In this case, the required amount of consumption of the energy generated by the vehicle can be reduced.
(9) A braking system according to the above mode (2), wherein at least one of the pressure-increasing device and the booster is a pneumatically operated device operable with compressed air, and the energy storing portion includes an air tank for storing the compressed air whose pressure is higher than an atmospheric level.
In the braking system according to the above mode (2), at least one of the pressure-increasing device and the booster is operated with compressed air stored in the air tank.
(10) A braking system according to any one of the above modes (1)-(9), further comprising an emergency enabling device operable when at least one of the brake-cylinder-pressure control device and the first pump device fails to normally function, for enabling the at least one of the pressure-increasing device and the booster to operate.
(11). A braking system according to any one of the above modes (1)-(10), wherein the brake cylinder is provided for braking a wheel of an automotive vehicle, and the brake-cylinder-pressure control device includes:
a solenoid-operated control valve disposed between the first hydraulic pressure source and the brake cylinder and operable according to an amount of electric energy supplied thereto; and
a control-valve control portion operable to control the amount of electric energy to be supplied to the solenoid-operated control valve, for controlling the pressure of the fluid in the brake cylinder such that the wheel is braked by the brake cylinder, so as to establish a deceleration value of the automotive vehicle which corresponds to the operating force of the brake operating member.
Where the braking system has a plurality of brake cylinders, the solenoid-operated control valve may be provided for each of the brake cylinders. Alternatively, a plurality of solenoid-operated control valves may be provided for respective brake cylinders.
The solenoid-operated control valve may be a solenoid-operated linear valve device capable of controlling the fluid pressure in the brake cylinder according to an amount of electric energy supplied to the linear valve device, as described below with respect to the following mode (12). Alternatively, the solenoid-operated control valve may be a solenoid-operated shut-off valve which is opened and closed as needed.
(12) A braking system according to any one of the above modes (1)-(11), comprising a plurality of brake cylinders as the brake cylinders, and wherein the brake-cylinder-pressure control device includes a plurality of solenoid-operated linear valve devices for controlling the fluid pressures in the plurality of brake cylinders according to amounts of electric energy supplied to the solenoid-operated linear valve devices.
(13) A braking system according to any one of the above modes (1)-(12), wherein said brake cylinder is provided for braking a wheel of an automotive vehicle, further comprising a regenerative braking device including an electric motor operable to apply a regenerative braking torque to the wheel, and wherein the brake-cylinder-pressure control device includes a cooperative control portion operable while the regenerative braking torque is applied to the wheel, to control the fluid pressure in the brake cylinder.
The braking system according to the present invention may be used on an electric vehicle or a hybrid vehicle. In this case, the electric motor provided to drive the vehicle is operable to apply a regenerative braking torque to a drive wheel of the vehicle, so that both the regenerative braking torque and a hydraulic braking torque generated by the brake cylinder are applied to the vehicle. Namely, the braking system is operated in a cooperative control mode in which the hydraulic braking torque is controlled such that a sum of the regenerative braking torque and the hydraulic braking torque approaches a total vehicle braking torque desired by the vehicle operator. Since it is desirable to maximize the regenerative braking torque for improving the energy efficiency, the hydraulic braking torque is generally controlled while the regenerative braking torque is held at the upper limit determined by the particular running condition of the vehicle. The desired total vehicle braking torque is generally determined to be a value that permits the operator""s desired deceleration value of the vehicle, which may be represented by the amount of operation of the brake operating member, for example.
Where at least one of the first pump device and the brake-cylinder-pressure control device fails to normally function while the braking system is operated in the cooperative control mode, the regenerative braking torque is usually zeroed. In this case, the brake cylinder is communicated with the second hydraulic pressure source. Where the second hydraulic pressure source includes the pressure-increasing device and/or the booster, the amount of change of the vehicle braking force corresponding to a given operating force of the brake operating member, which change is unexpected to the vehicle operator, can be reduced.
(14) A braking system according to any one of the above modes (1)-(13), wherein the emergency communication device includes a solenoid-operated shut-off valve which is placed in an open state for fluid communication between the brake cylinder and the second hydraulic pressure source when no electric energy is supplied to the solenoid-operated shut-off valve, and in a closed state for disconnection of the brake cylinder from the second hydraulic pressure source when an electric energy is supplied to the solenoid-operated shut-off valve, the emergency communication device further including a valve control portion for applying the electric energy to the solenoid-operated shut-off valve while the first pump device and the brake-cylinder-pressure control device are normal.
The solenoid-operated valve may or may not be included in the brake-cylinder-pressure control device.
The emergency communication device may include a mechanically operated change valve rather than the solenoid-operated shut-off valve described above. The change valve has a first state in which the brake cylinder is disconnected from the second hydraulic pressure source and is held in fluid communication with the first hydraulic pressure source, and a second state in which the brake cylinder is disconnected from the first hydraulic pressure source and is held in fluid communication with the second hydraulic pressure source. The change valve is mechanically switched from the first state to the second state when the output fluid pressure of the first hydraulic pressure source becomes lower than a lower limit below which the first pump device is estimated to be unable to normally function, or becomes lower than the output fluid pressure of the second hydraulic pressure source.
(15) A braking system according to any one of the above modes (3)-(6), wherein the first hydraulic pressure source includes a plurality of pump devices including the first pump device, the fluid pressurized by at least one of the plurality of pump devices being stored in the first accumulator.
In the braking system according to the above mode (15) wherein the first hydraulic pressure source includes a plurality of pump devices, the fluid pressurized by at least one of the pump devices is stored in the first pump device. When the first pump device fails to normally function, the fluid pressurized by the other normally functioning pump device or devices, if any, may be delivered directly to the second hydraulic pressure source, without the pressurized fluid being once stored in the first accumulator.
(16) A braking system according to the above mode (15), wherein the plurality of pump devices includes at least one low-pressure pump device and at least one high-pressure pump device the having a higher maximum delivery pressure and a lower maximum delivery rate than the at least one low-pressure pump device.
Where the maximum delivery pressure of the low-pressure pump device is higher than the brake cylinder pressure required when the brake operating member is operated with an ordinary operating force, the pressurized fluid delivered from the low-pressure pump is more frequently used than the pressurized fluid delivered from the high-pressure pump device. In this case, it is more effective to arrange the braking system such that the first accumulator stores the pressurized fluid delivered from the high-pressure pump device, rather than the pressurized fluid delivered from the low-pressure pump device, since the pressurized fluid delivered from the high-pressure pump device can be stored in the first accumulator with higher stability, owing to the comparatively infrequent use of the output pressure of the high-pressure pump device for activating the brake cylinder during normal operation of the braking system.
Further, the delivery pressure and rate of the low-pressure pump device can be controlled by controlling the operating state of an electric motor provided in the low-pressure pump device. By controlling the delivery pressure and rate of the low-pressure pump device, the fluid pressure in the brake cylinder can be controlled. In this case, the control device for controlling the low-pressure pump device serves as the brake-cylinder-pressure control device, pressure control valves may be eliminated.
The pump used in each of the plurality of pump devices may be a gear pump or a plunger pump. Where the low-pressure pump device uses a gear pump, the pressure pulsation and operating noise of the low-pressure pump device can be reduced.
(17) A braking system comprising:
a brake cylinder;
a first hydraulic pressure source including a first pump device and a first accumulator for storing a working fluid pressurized by the first pump device;
a second hydraulic pressure source operable in response to an operation of a rake operating member, to pressurize the fluid to a pressure higher than a value corresponding to an operating force acting on the brake operating member, while utilizing the pressurized fluid stored in the first accumulator;
a brake-cylinder-pressure control device operable when the brake cylinder is disconnected from the second hydraulic pressure source, to control the pressure of the fluid pressurized by the first hydraulic pressure source, such that a pressure of the fluid in the brake cylinder is controlled to a value determined on the basis of the operating force;
an emergency communication device operable when at least one of the brake-cylinder-pressure control device and the first pump device fails to normally function, to hold the brake cylinder in communication with the second hydraulic pressure source.
The braking system according to the above mode (17) may include the technical feature according to any one of the above modes (1)-(16).
(18) A braking system according to the above mode (17), wherein the second hydraulic pressure source includes a hydraulic booster hydraulically operated to boost the operating force of the brake operating member, while utilizing the pressurized fluid stored in the first accumulator.
(19) A braking system according to the above mode (17) or (19), wherein the second hydraulic pressure source includes:
a master cylinder operable in response to the operation of the brake operating member, to pressurize the fluid to a pressure corresponding the operating force of the brake operating member; and
a pressure regulator connected to the master cylinder, the first accumulator and the brake cylinder and mechanically operable to increase the pressure of the pressurized fluid received from the master cylinder while utilizing the pressurized fluid stored in the first accumulator, and apply the increased pressure to the brake cylinder.
In the braking system according to the above mode (19) wherein the second hydraulic pressure source includes the mechanically operated pressure regulator to increase the pressure of the fluid received from the master cylinder, the pressure regulator is operable even when the braking system has an electrical failure or defect. Further, the second hydraulic pressure source may be made simpler in construction than in the braking system wherein the second hydraulic pressure source includes a hydraulic booster.
(20) A braking system according to the above mode (19), wherein the second hydraulic pressure source further includes a communication switching valve disposed between the pressure regulator and said brake cylinder and operable to disconnect the brake cylinder from said pressure regulator and bring the brake cylinder into fluid communication with the master cylinder when the fluid pressure of the pressure regulator becomes lower than a lower limit which is determined by and is not higher than the fluid pressure pressurized by the master cylinder.
The communication switching device may disconnect the brake cylinder from the pressure regulator and bring the brake cylinder into fluid communication with the master cylinder when the fluid pressure of the pressure regulator become lower than the fluid pressure of the master cylinder, or becomes lower than the fluid pressure of the master cylinder by more than a predetermined amount. That is, the lower limit indicated above may be equal to the fluid pressure of the master cylinder, or may be lower than the fluid pressure of the master cylinder by a predetermined amount. In either of these two cases, the communication switching device is mechanically switched for establishing fluid communication of the brake cylinder with the master cylinder, with high stability, when the fluid pressure of the pressure regulator becomes lower than the lower limit, even in the event of an electrical failure of the braking system.
However, the pressure regulator may be constructed such that the brake cylinder is communicated with the master cylinder when the fluid pressure of the pressure regulator becomes lower than a predetermined lower limit. Where this lower limit is determined by the pressure of the fluid pressurized by the master cylinder during a normal operation of the brake operating member, the pressure regulator may be considered to incorporate the communication switching device provided according to the above mode (20).
(21) A braking system according to any one of the above modes (17)-(20), further comprising a high-pressure-fluid supply control device which permits a supply of the pressurized fluid from the first accumulator to the second hydraulic pressure source when at least one of the first pump device and the brake-cylinder-pressure control device fails to normally function, and inhibits the supply when the first pump device and the brake-cylinder-pressure control device are normal.
The high-pressure-fluid supply control device may include a solenoid-operated shut-off valve which is disposed between the first accumulator and the second hydraulic pressure source, for instance, and which is opened when at least one of the first pump device and the brake-cylinder-pressure control device fails to normally function. This shut-off valve is preferably a normally open valve when a solenoid coil of the shut-off valve is de-energized.
(22) A braking system comprising:
a brake cylinder;
a first hydraulic pressure source including a first pump device and a first accumulator for storing a working fluid pressurized by the first pump device;
a second accumulator;
a second hydraulic pressure source operable in response to an operation of a rake operating member, to pressurize the fluid to a pressure higher than a value corresponding to an operating force acting on the brake operating member, while utilizing a pressurized fluid stored in the second accumulator;
a brake-cylinder-pressure control device operable to control the pressure of the fluid pressurized by the first hydraulic pressure source, such that a pressure of the fluid in the brake cylinder is controlled to a value determined on the basis of the operating force;
an emergency communication device operable when at least one of the brake-cylinder-pressure control device and the first pump device fails to normally function, to hold the brake cylinder in communication with the second hydraulic pressure source.
In the braking system according to the above mode (22) of this invention, the second accumulator is provided exclusively for use with the second hydraulic pressure source, in addition to the first hydraulic pressure source included in the first hydraulic pressure source. This arrangement assures improved operating reliability of the braking system than in the braking system wherein the first accumulator is utilized for operating the first hydraulic pressure source.
When the brake-cylinder-pressure control device and the first pump device are both normal (while the fluid pressure in the brake cylinder is controlled by the brake-cylinder-pressure control device), the brake cylinder may be either disconnected from or communicated with the second hydraulic pressure source.
The braking system according to the above mode (22) may include the technical feature according to any one of the above modes (1)-(21).
(23) A braking system according to the above mode (22), further comprising a second pump device operable to pressurize the working fluid, and wherein the second accumulator stores the fluid pressurized by the second pump device.
In the braking system according to the above mode (23) wherein the second accumulator stores the fluid pressurized by the second pump device provided exclusively for the second hydraulic pressure source, the operating reliability is further improved. Since the pressurized fluid stored in the second accumulator is used exclusively and only for operating the brake cylinder when at least one of the brake-cylinder-pressure control device and the first pump device fails to normally function, the amount of energy stored in the second accumulator is larger than that stored in the first accumulator, so that the pressure-increasing device and/or the booster of the second hydraulic pressure source can be operated for a longer period of time after the brake-cylinder-pressure control device and/or the first pump device fail or fails.
(24) A braking system according to the above mode (22), further comprising:
a fluid passage connecting the second accumulator and the first pump device;
a switch valve disposed in the fluid passage, the switch valve being operated from an open state for fluid communication of the second accumulator with the first pump device to a closed state for inhibiting the communication of the second accumulator with the first pump device when at least one of the brake-cylinder-pressure control device and the first pump device fails to normally function.
The second pump device need not be provided in addition to the first pump device, since the second accumulator may be arranged to store the fluid pressurized by the first pump device. The braking system according to the above mode (24) including only the first pump device is smaller in size and more economical to manufacture, than the braking system including the first and second pump devices.
When the switch valve is placed in its open state, the fluid pressurized by the first pump device can be supplied to the second accumulator. When the switch valve is placed in the closed state, the pressurized fluid stored in the second accumulator is prevented from being undesirably delivered back to the first hydraulic pressure source, so that the pressure-increasing device and/or the booster of the second hydraulic pressure source can be operated with stability.
When the brake-cylinder-pressure control device is defective, for instance, the pressurized fluid may leak through the first hydraulic pressure source and the defective brake-cylinder-pressure control device. While the pressurized fluid is not supplied from the first pump device to the second accumulator, it is preferable to disconnect the second accumulator from the first pump device.
(25) A braking system comprising:
a brake cylinder;
a first hydraulic pressure source including a pump device operable to pressurize a working fluid;
a second hydraulic pressure source operable in response to an operation of a brake operating member, to pressurize the fluid to a pressure higher than a value corresponding to an operating force acting on the brake operating member, the second hydraulic pressure source including at least one of a booster for boosting the operating force of the brake operating member, and a pressure-increasing device for increasing the pressure of the fluid pressurized when the brake operating member is operated;
a brake-cylinder-pressure control device operable to control the pressure of the fluid pressurized by the first hydraulic pressure source such that a pressure of the fluid in the brake cylinder is controlled to be a value determined on the basis of the operating force; and
an emergency enabling device operable when at least one of the brake-cylinder-pressure control device and the pump device fails to normally function, for permitting an operation of the at least one of the brake-cylinder-pressure control device and the pump device, which operation has been inhibited.
The operation of at least one of the pressure-increasing device and/or the booster of the second hydraulic pressure source is required only when and after at least one of the brake-cylinder-pressure control device and the pump device fails to normally function. In other words, the operation of the pressure-increasing device and/or the booster is not required while the brake-cylinder-pressure control device and the pump device are both normal. Since this operation of the pressure-increasing device and/or the booster is inhibited by the emergency enabling device, the amount of energy consumption by the braking system is reduced according to the above mode (25) of the invention.
When at least one of the brake-cylinder-pressure control device and the pump device fails to normally function during an operation of the brake pedal, at least one of the pressure-increasing device and the booster is immediately activated by the emergency enabling device. In this sense, the emergency enabling device may be considered to be an emergency activating device for activating the pressure-increasing device and/or the booster.
The braking system according to the above mode (25) may include the technical feature according to any one of the above modes (1)-(24).
(26) A braking system comprising:
a brake cylinder;
a first hydraulic pressure source including a pump device operable to pressurize a working fluid;
a second hydraulic pressure source operable in response to an operation of a brake operating member, to pressurize the fluid, the second hydraulic pressure source including a booster for boosting an operating force of a brake operating member;
a brake-cylinder-pressure control device operable to control the pressure of the fluid pressurized by the first hydraulic pressure source such that a pressure of the fluid in the brake cylinder is controlled to be a value determined on the basis of the operating force; and
an emergency boosting-ratio control device operable when at least one of the brake-cylinder-pressure control device and the pump device fails to normally function, for controlling a boosting ratio of the booster while the brake cylinder is held in communication with said second hydraulic pressure source.
In the braking system according to the above mode (26) of this invention, the second hydraulic pressure source includes a booster whose boosting ratio can be controlled to control the fluid pressure in the brake cylinder, even when at least one of the brake-cylinder-pressure control device and the pump device fails to normally function.
The emergency boosting-ratio control device, which is capable of controlling the boosting ratio of the booster when the pump device and/or the brake-cylinder-pressure control device is/are defective, is desirably operated with an energy source which is separate from an energy source used for the pump device and the brake-cylinder-pressure control device.
The braking system according to the above mode (26) may include the technical feature according to any one of the above modes (1)-(25).
(27) A braking system comprising:
a brake cylinder;
a first hydraulic pressure source including a pump device operable to pressurize a working fluid;
a second hydraulic pressure source operable in response to an operation of a brake operating member, to pressurize the fluid to a pressure higher than a value corresponding to an operating force acting on the brake operating member, while utilizing a highly pressurized fluid;
a brake-cylinder-pressure control device operable when the brake cylinder is disconnected from the second hydraulic pressure source, to control the pressure of the fluid pressurized by the first hydraulic pressure source, such that a pressure of the fluid in the brake cylinder is controlled to a value determined on the basis of the operating force; and
an emergency communication device operable when at least one of the brake-cylinder-pressure control device and the pump device fails to normally function, to hold the brake cylinder in communication with the second hydraulic pressure source.
In the braking system according to the above mode (27) of this invention, the fluid pressurized by the first hydraulic pressure source is controlled to control fluid pressure in the brake cylinder, with the brake cylinder being disconnected from the second hydraulic pressure source, while the braking system is normal. When at least one of the brake-cylinder-pressure control device and the pump device fails to normally function, the brake cylinder is communicated with the second hydraulic pressure source. The second hydraulic pressure source may include a hydraulic booster or a pressure-increase device.
The braking system according to the above mode (17) may include the technical feature according to any one of the above modes (1)-(26).